Will learning theory hurt my creativity or improvisation?
No: theory names options, it does not remove them. Knowing why things work lets you break rules on purpose instead of by accident.
A bigger vocabulary never made anyone worse at conversation. Theory is vocabulary: it adds choices, it does not delete the ones you had.
The musicians you admire for "playing free" almost all know the map well enough to leave it on purpose.
The fear usually comes from a real experience: mid-learning, you become conscious of mechanics and briefly play stiffer, the way thinking about walking makes you walk strangely. It passes as the knowledge automates, and you come out with more options, not fewer.
Theory is descriptive: it explains why the things you already love sound the way they do. Learning that the trick you discovered by ear is "a deceptive cadence" does not un-discover it; it hands you ten neighboring tricks.
The practical guard: keep creating while you learn. Alternate analysis sessions with play sessions where you deliberately ignore the names.
Cognitively, skills pass through a conscious-competence phase where explicit knowledge and fluent execution compete for attention; that phase, not theory itself, is the stiffness people report. Automatization through use dissolves it.
Improvisation research consistently shows expert improvisers operating on deeply internalized pattern libraries: what feels like pure spontaneity is fast recombination of learned material. Theory accelerates building exactly that library.
The productive stance: treat rules as descriptions of expectations. Music moves listeners by setting up expectations and choosing when to satisfy or break them, and you can only choose deliberately if you know what the expectation is.